The present invention is related to a technique for drawing on an optical disk.
Among optical disks such as CD-R (Compact Disk-Recordable), CD-RW (Compact Disk-Rewritable), and DVD-R (Digital Versatile Disk-Recordable), since contents of recorded data cannot be discriminated from each other by human eyes, it is practically difficult to discriminate the respective optical disks from each other based upon outer appearances of these optical disks if labels are not attached, but also labels are not printed thereon. As a consequence, the following technical ideas have been proposed: That is, since characters, symbols, or figures/pictures are drawn on optical disks, these optical disks can be simply discriminated from each other based upon the outer appearances thereof. Also, technical ideas capable of rewriting images drawn on optical disks have been proposed. For instance, JP-A-2006-155812 has proposed such a technique that after an image drawn on an optical disk is once erased, the image is again drawn. Also, JP-A-2003-16649 has described another technique capable of performing a gradation representation of an image based upon dimensions of bits and duty ratios.
However, in the technique described in JP-A-2006-155812, after the existing image is erased, a new image is formed. As a result, there is such a problem that a lengthy time is required in order to form the image. Also, in the technique described in JP-A-2003-16649, the gradation representation is determined based upon the dimensions of the bits, or the duty ratios. As a result, assuming now that a direct overwriting operation is carried out, there is such a problem that erasing remainders occur, so that the gradation is disturbed.